Organic semiconductors are being developed for a number of different electronic applications. The structure of organic electroluminescent devices (OLEDs) in which these organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. However, further improvements are still desirable for use of these devices for high-quality and long-lived displays. Thus, there is currently still a need for improvement, in particular, in the lifetime and efficiency of blue-emitting organic electroluminescent devices. Furthermore, it is necessary for the compounds to have high thermal stability and a high glass-transition temperature and to be sublimable without decomposition. In particular for use at elevated temperature, a high glass-transition temperature is essential for achieving long lifetimes.
There therefore continues to be a demand for improved materials, for example host materials for fluorescent and phosphorescent emitters, but further improvements are also desirable, in particular, in charge-transport materials, i.e. hole- and electron-transport materials, charge-blocking materials and exciton-blocking materials. The properties of these materials in particular are frequently limiting for the lifetime and efficiency of the organic electroluminescent device.